The concentration of oxidizing gases in the air, such as the concentration of nitrogen dioxide or ozone, is one of several indicators for assessing the degree of air pollution. The main sources of oxidizing gases in the air are vehicle exhaust and factory exhaust. Recent researches show that excessive concentrations of oxidizing gases in the air can cause adverse effects on the respiratory system of the human body, such as irritation of the respiratory tract and reduction of pulmonary function, and even worsen the conditions of chronic lung diseases such as asthma, chronic bronchitis and emphysema. Therefore, with the increasing emphasis on air pollution prevention and control, the requirement for real-time monitoring of the concentration of oxidizing gases in the air also increases accordingly.
Although the conventional oxidizing gas detecting apparatus has the advantages of high sensitivity and high accuracy, it has the disadvantages of bulky size, complex structure expensive price, and is not suitable for real-time monitoring of environmental gases. The commonly used real-time monitoring apparatus for environmental gases is a metal oxide semiconductor detector. The metal oxide semiconductor detector has the advantages of small size, low cost, and good weathering resistance, but it also has the disadvantage that the detecting result is easily interfered by the reducing gas. In addition, the commonly used metal oxide semiconductor detector needs a high temperature such as 200 degrees Celsius and above to perform the concentration detection for trace gases, resulting the interference of the reducing gas being more obvious. Therefore, in order to satisfy the increasing demand of real-time monitoring of the concentration of oxidizing gas, it is necessary to develop the oxidizing gas detecting apparatus which has the ability to detect concentration of the trace gases and the detection result is not easily affected by the concentration of the reducing gas.